List of non-native arthropods in North America.

Introduction

Ever since the first European explorers arrived in the American continent, plants and animals have been arriving along with them. It is estimated that more than two thousand (2,273) species of insects and arachnids have set residence in this continent, according to the North American Non-Indigenous Arthropod Database of the USDA or NANIAD.
Some were brought intentionally, others arrived on their own. With the increase in traveling and international commerce, the numbers of introduced species probably keeps growing even faster than in earlier times. Some of them become invasive, wreaking havoc in local ecosystems, not just the ones that were introduced accidentally, but also some that were brought intentionally for a variety of reasons and later on managed to escape and spread beyond control. More insects have been introduced intentionally than otherwise, especially to serve as biological controls. It is estimated that over 1700 species have entered this way; most of them are parasitoids or predators of pests.
Among the earliest pests that arrived in colonial times probably were the bed bug Cimex lectularius, cockroaches and the mosquito Aedes aegypti. Probably the earliest insects that were brought intentionally were the domestic bee Apis mellifera and the silk worm Bombyx mori. The silk worm is of no concern to us because, after thousands of years of domestication, it has lost its ability to survive on its own, and it is not found in nature. The honey bee on the other hand is a very resourceful and adaptable creature that has escaped domestication repeatedly and set up housekeeping in tree holes, other natural cavities and even hollow walls, much to the delight of bears and other honey-eating animals. Nowadays it is probably established in most states and there is no way to tell the impact that populations of domestic bees have had on native bees and on native flowers.
In addition to the comprehensive list issued by NANIAD there are a few other resources on the internet that may be of interest here:
A report issued by USDA Forest Service in 1994 lists 368 immigrant plant-eating insects. See:Immigrant Phytophagous Insects: an Annotated List.
Invasive.org, (a joint project of: The Bugwood Network, USDA Forest Service and USDA APHIS PPQ, the University of Georgia – Warnell School of Forest Resources and College of Agricultural and Environmental Sciences – Dept. of Entomology) lists 152 species of invasive insects. See Invasive insects.
A report of the University of Florida Invasive Insects (Adventive Pests Insects) in Florida lists 150 species of insects and 35 species of arachnids considered invasive in that state. Note that some of them were introduced to Florida from some other states, not from abroad.
The same thing applies to Invasive Species Resource List provided by the University of Pennsylvania.
Cornell University has a list of some insects used as biocontrols. See Biocontrols. Many of them, but not all have been introduced from other countries.
Perhaps the most complete list of species intentionally introduced as biocontrols is ROBO – Releases of Beneficial Organisms in the United States and Territories. It also includes a list of “target” species, the hosts of prey of the beneficial ones; most of them are undesirable non-natives.
Here, at BugGuide we have approximately 80 species of introduced insects and spiders (as of September 2005) and the numbers keep growing. I think that a list of non-native insects and arachnids with links to the corresponding pages would be of great value. I hope that everybody helps adding species that I missed or new ones as they are added to the guide. I hope to get your help with taxonomic issues, such as the proper sorting of families within larger taxa.

This list includes only non-native species featured in BugGuide in which there is a high degree of certainty of having been introduced. Others have been omitted, but will be added if somebody confirms that they are not native. For each species there is a link to the pertinent page with additional information if available. Please, notice that for practical reasons, I have not attempted to lists species that have been introduced from one region to another within North America. These introductions are no less important but would be difficult to include them here.

"Homidia socia Börner, 1909 — TX IN [= trogloxene introduced, not state list -jfc]
Locality: Spider Cave
This is an introduced species. Almost all species of Homidia are restricted to East Asia and Oceania; only two (H. socia and H. sauteri) are known from North America. The oldest record of H. socia in North America appears to be from 1970, from Georgia (K. Christiansen, Collembola records database). The historical collection of springtails at the Illinois Natural History Survey that goes back to the second half of the 1800s, does not include representatives of this species, despite it now being the most common form found in grasses growing along country roads in Champaign County. Homidia socia was first noticed in a cave in Johnson County, southern Illinois, in 1973 (Christiansen and Bellinger, 1980, 1998; K. Christiansen, Collembola records database) and in Champaign County by the senior author in 1988. The species is also known from caves in Harrison and Crawford counties, Indiana."

"This species was originally described from the Washington, D.C., area, but currently it is known to occur around the world in protected habitats such as greenhouses and caves (Chen and Christiansen, 1997). The genus Coecobrya is almost exclusively East Asian in distribution (Chen and Christiansen, 1997), and it is likely that C. tenebricosa represents an early introduction, during historic times, into North America."

In addition to the soil centipede Geophilus flavus (http://bugguide.net/node/view/925018) mentioned by Tom Murray below, there are a few more European centipedes that are found in North America. A known introduction is Lithobius microps (http://bugguide.net/node/view/907459).

BUT ...

Two European species which are also found in North America, are believed to be introduced, however, there isn't much evidence that they aren't naturally Holarctic species. They are Schendyla nemorensis (http://bugguide.net/node/view/905726) and Lamyctes emarginatus (http://bugguide.net/node/view/907457).

Perhaps someday genetic work will show conclusively which species are native and which are introduced, but for now we can only guess. I am particularly suspicious that L. emarginatus may naturally occur in North America because it is parthenogenetic and could easily have become established by arriving on "rafts," and also because it appears to have a sister species in North America (L. pius, but it may be a synonym). Schendyla nemorensis I also suspect is native based on its continent-wide distribution, all the way to Alaska.

Just a note that under family Agelenidae in the spider section, Tegenaria atrica and Tegenaria gigantea were synonymized and then moved to a new genus. So the new name is Eratigena atrica. When I combined/moved the species pages in the guide, I did it wrong with T. atrica, so unfortunately that old link doesn't just re-route to the right place. =(
Also, Tegenaria agrestis is now Eratigena agrestis.

Thanks, Beatriz!
I keep meaning to do another thorough sweep for other introductions, but just remembered this one:Arctosa perita (Lycosidae) - looks like the first wolf spider for the list! The literature doesn't say what country it's probably from (just says "introduced in recent decades"), but I assume Europe even though it's also found in Asia and North Africa.

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